Minimal effects of ultraviolet light supplementation on egg production, egg and bone quality, and health during early lay of laying hens

Chicken vision is sensitive to ultraviolet (UV) light containing the UVA spectrum, while UVB plays a key role in the endogenous production of vitamin D₃. However, commercially available light sources are typically deficient in the UV spectrum and thus may not adequately fulfill the lighting requirements of indoor-housed laying hens. We hypothesized that supplementary UVB light may improve egg production and egg quality, and bone health during early lay relative to UVA supplementation or standard control lighting. To investigate the effects of UV light supplementation, an experiment was conducted on 252 ISA Brown hens during 16 to 27 weeks of age. Birds were housed in eighteen pens (14 hens/pen) under three different light treatment groups each with six replications: (i) UVO: standard control lighting with LED white light, (ii) UVA: control lighting plus supplemental daylight with an avian bulb, and (iii) UVA/B: control lighting plus a supplemental full spectrum reptile bulb containing both UVA and UVB wavelengths. Hen-day egg production and egg quality, blood parameters including plasma Ca and P, and serum 25(OH)D₃, and hen body weight and external health scoring were measured at different age points; while bone quality was assessed at the end of the experiment at 27 weeks. Data were analyzed in JMP® 16.0 using general linear mixed models with α level set at 0.05. Results showed that UVA and UVA/B supplemented birds reached sexual maturity (50% production) 3 and 1 day earlier, respectively, than control birds. There was a trend for UV lights to increase hen-day egg production (P = 0.06). Among egg quality traits, only eggshell reflectivity and yolk index were affected by UV lights (P = 0.02 and 0.01, respectively); however, most of the egg quality traits changed over age (all P < 0.01). Post-hoc tests showed higher serum 25(OH)D₃ in the UVA/B group relative to control hens (P < 0.05); but there was no treatment effect on plasma Ca and P or on bone quality parameters (all P > 0.05). A significant interaction was observed between light treatment and age for the number of comb wounds (P = 0.0004), with the UV supplemented hens showing more comb wounds after 24 weeks. These results demonstrated that supplemental UVA/B light had minimal effects on egg production and egg quality, whereas, UVA/B exposure may increase vitamin D₃ synthesis during the early laying period. The optimum duration of exposure and level of intensity needs to be determined to ensure these benefits.